This invention relates generally to machines for transferring bulk material and, more particularly, to an apparatus and method for determining the weight of the bulk material being transferred.
Machines such as loaders are used generally to transfer bulk material from a stock pile onto transport machines such as truck or railroad cars. In such machine loading applications it is desirable that the transport machines are loaded to, but not over, their maximum rated capacity. Underloading causes inefficiency in the material hauling cycle and under utilization of the transport machines. Overloading causes additional maintenance cost and extra wear on the truck tires and suspension systems. Furthermore, the overloaded material may need to be unloaded to decrease load weight, causing additional expense. Therefore, accurate payload measurement is desirable.
Payload measurement is also desirable as a method of determining operation productivity. The ability to accumulate the weight of the material loaded during a single shift, during a twenty-four hour period, or during any other time period is valuable to an operations manager.
Payload measurement systems utilizing sensed lift cylinder pressures have been developed that enable the system to be calibrated using known weights and then used to determine payload weight during the operation of the machine. This measurement method is dependent on the pressure to weight ratio remaining consistent between the time the machine is calibrated and the time the machine is measuring an unknown load. This consistency is compromised when the working fluid viscosity deviates from the fluid viscosity at calibration time. Some weight measurement systems, such as that disclosed in U.S. Pat. No. 5,606,516 issued to Douglas et al. On Feb. 25, 1997, have been developed which attempt to account for changes in ambient temperature, or changes to the temperature of a pressure transducer. The system disclosed in Douglas applies to a weighing platform, or scale, adapted to determine the weight of a machine, such as a truck. Douglas discloses incorporating a temperature sensor to determine the temperature of the pressure transducers and hydraulic transducers used. A pressure transducer may change its sensing characteristics based on changes in its core temperature. Changes in temperature of the transducers may occur due to changes in ambient temperature and possibly changes in the fluid temperature passing through the transducer. However changes in the temperature of the transducer, even if due in part to fluid temperature changes, is an ineffective method of accounting for changes to the actuating fluid viscosity during the payload measurements. For example, there is not a direct correlation between fluid viscosity changes, and temperature changes of the pressure transducer itself. This is due in part to the fact that ambient temperatures effect the temperature of the pressure transducer. In addition, subtle changes in actuating fluid temperature may result in noticeable changes in the viscosity of the fluid, but may not result in any temperature variations of the pressure transducer itself.
Changes in fluid viscosity have a noticeable effect on payload calculations. The viscosity of the fluid changes as the temperature changes, as the actuating fluid degrades due to use or time, or if a fluid having a different viscosity is added to the hydraulic circuit. Changes in fluid viscosity effect the pressure of the fluid as the fluid travels through the valves, cylinders, pump and tank of the hydraulic circuit. Therefore, while pressure sensors may deliver accurate readings of the pressure when the temperature changes, the pressure does not correlate with the same payload weight measured at a different temperature, i.e., a different viscosity.
The present invention is directed to overcoming one or more of the problems set forth above.
In one aspect of the present invention, a method for dynamically measuring a payload weight for a machine is disclosed. The machine has at least one cylinder for elevating a payload carrier. The cylinder is connected to a fluid circuit having an actuating fluid. The method includes the steps of sensing a first plurality of pressure values of the actuating fluid during a lifting of a first payload; sensing a second plurality of pressure values of the actuating fluid during a lifting of a second payload; sensing a third plurality of pressure values of the actuating fluid during a lifting of a third payload; establishing a parameter indicative of the viscosity of the actuating fluid associated with the third lift; and establishing a payload weight of the third payload in response to the viscosity indicative parameter, and the first and second and third plurality of actuating fluid pressure values.
In another aspect of the present invention, an apparatus configured to dynamically measure a payload weight for a machine is disclosed. The machine has at least one cylinder for elevating a payload carrier. The cylinder is connected to a fluid circuit having an actuating fluid. The apparatus includes a pressure sensor configured to sense a pressure of the actuating fluid associated with the cylinder and responsively generating a pressure signal; an extension sensor configured to sense a characteristic indicative of an extension of the cylinder and responsively generating an extension signal; and a controller configured to receive a plurality of the extension, and pressure signals, at least one viscosity indicative parameter signal, associated with a first lift of a first payload having a first payload weight, a second lift of a second payload having a second payload weight, and a third lift of a third payload having a third payload weight, and determine a weight of said third payload in response to the plurality of pressure signals, the plurality of extension signals, the viscosity indicative parameter, and, the first payload weight and the second payload weight.